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divide.py
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divide.py
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from __future__ import absolute_import
__author__ = "John Kirkham <kirkhamj@janelia.hhmi.org>"
__date__ = "$Dec 08, 2016 15:26:16 GMT-0500$"
import itertools
import operator
import warnings
import kenjutsu.format
def split_blocks(space_shape, block_shape, block_halo=None):
"""
Return a list of slicings to cut each block out of an array or other.
Takes an array with ``space_shape`` and ``block_shape`` for every
dimension and a ``block_halo`` to extend each block on each side. From
this, it can compute slicings to use for cutting each block out from
the original array, HDF5 dataset or other.
Note:
Blocks on the boundary that cannot extend the full range will
be truncated to the largest block that will fit. This will raise
a warning, which can be converted to an exception, if needed.
Args:
space_shape(tuple): Shape of array to slice
block_shape(tuple): Size of each block to take
block_halo(tuple): Halo to tack on to each block
Returns:
collections.Sequence of \
tuples of slices: Provides tuples of slices for \
retrieving blocks.
Examples:
>>> split_blocks(
... (2, 3,), (1, 1,), (1, 1,)
... ) #doctest: +NORMALIZE_WHITESPACE
([(slice(0, 1, 1), slice(0, 1, 1)),
(slice(0, 1, 1), slice(1, 2, 1)),
(slice(0, 1, 1), slice(2, 3, 1)),
(slice(1, 2, 1), slice(0, 1, 1)),
(slice(1, 2, 1), slice(1, 2, 1)),
(slice(1, 2, 1), slice(2, 3, 1))],
<BLANKLINE>
[(slice(0, 2, 1), slice(0, 2, 1)),
(slice(0, 2, 1), slice(0, 3, 1)),
(slice(0, 2, 1), slice(1, 3, 1)),
(slice(0, 2, 1), slice(0, 2, 1)),
(slice(0, 2, 1), slice(0, 3, 1)),
(slice(0, 2, 1), slice(1, 3, 1))],
<BLANKLINE>
[(slice(0, 1, 1), slice(0, 1, 1)),
(slice(0, 1, 1), slice(1, 2, 1)),
(slice(0, 1, 1), slice(1, 2, 1)),
(slice(1, 2, 1), slice(0, 1, 1)),
(slice(1, 2, 1), slice(1, 2, 1)),
(slice(1, 2, 1), slice(1, 2, 1))])
"""
try:
irange = xrange
except NameError:
irange = range
try:
from itertools import ifilter, imap
except ImportError:
ifilter, imap = filter, map
if block_halo is not None:
if not (len(space_shape) == len(block_shape) == len(block_halo)):
raise ValueError(
"The dimensions of `space_shape`, `block_shape`, and"
" `block_halo` should be the same."
)
else:
if not (len(space_shape) == len(block_shape)):
raise ValueError(
"The dimensions of `space_shape` and `block_shape` should be"
" the same."
)
block_halo = tuple()
for i in irange(len(space_shape)):
block_halo += (0,)
vec_add = lambda a, b: imap(operator.add, a, b)
vec_sub = lambda a, b: imap(operator.sub, a, b)
vec_mul = lambda a, b: imap(operator.mul, a, b)
vec_mod = lambda a, b: imap(operator.mod, a, b)
vec_nonzero = lambda a: \
imap(lambda _: _[0], ifilter(lambda _: _[1], enumerate(a)))
vec_str = lambda a: imap(str, a)
vec_clip_floor = lambda a, a_min: \
imap(lambda _: _ if _ >= a_min else a_min, a)
vec_clip_ceil = lambda a, a_max: \
imap(lambda _: _ if _ <= a_max else a_max, a)
vec_clip = lambda a, a_min, a_max: \
vec_clip_ceil(vec_clip_floor(a, a_min), a_max)
uneven_block_division = tuple(vec_mod(space_shape, block_shape))
if any(uneven_block_division):
uneven_block_division_str = vec_nonzero(uneven_block_division)
uneven_block_division_str = vec_str(uneven_block_division_str)
uneven_block_division_str = ", ".join(uneven_block_division_str)
warnings.warn(
"Blocks will not evenly divide the array." +
" The following dimensions will be unevenly divided: %s." %
uneven_block_division_str,
RuntimeWarning
)
ranges_per_dim = []
haloed_ranges_per_dim = []
trimmed_halos_per_dim = []
for each_dim in irange(len(space_shape)):
# Construct each block using the block size given. Allow to spill over.
if block_shape[each_dim] == -1:
block_shape = (block_shape[:each_dim] +
space_shape[each_dim:each_dim+1] +
block_shape[each_dim+1:])
# Generate block ranges.
a_range = []
for i in irange(2):
offset = i * block_shape[each_dim]
this_range = irange(
offset,
offset + space_shape[each_dim],
block_shape[each_dim]
)
a_range.append(list(this_range))
# Add the halo to each block on both sides.
a_range_haloed = []
for i in irange(2):
sign = 2 * i - 1
haloed = vec_mul(
itertools.repeat(sign, len(a_range[i])),
itertools.repeat(block_halo[each_dim], len(a_range[i])),
)
haloed = vec_add(a_range[i], haloed)
haloed = vec_clip(haloed, 0, space_shape[each_dim])
a_range_haloed.append(list(haloed))
# Compute how to trim the halo off of each block.
# Clip each block to the boundaries.
a_trimmed_halo = []
for i in irange(2):
trimmed = vec_sub(a_range[i], a_range_haloed[0])
a_trimmed_halo.append(list(trimmed))
a_range[i] = list(vec_clip(a_range[i], 0, space_shape[each_dim]))
# Convert all ranges to slices for easier use.
a_range = tuple(imap(slice, *a_range))
a_range_haloed = tuple(imap(slice, *a_range_haloed))
a_trimmed_halo = tuple(imap(slice, *a_trimmed_halo))
# Format all slices.
a_range = kenjutsu.format.reformat_slices(a_range)
a_range_haloed = kenjutsu.format.reformat_slices(a_range_haloed)
a_trimmed_halo = kenjutsu.format.reformat_slices(a_trimmed_halo)
# Collect all blocks
ranges_per_dim.append(a_range)
haloed_ranges_per_dim.append(a_range_haloed)
trimmed_halos_per_dim.append(a_trimmed_halo)
# Take all combinations of all ranges to get blocks.
blocks = list(itertools.product(*ranges_per_dim))
haloed_blocks = list(itertools.product(*haloed_ranges_per_dim))
trimmed_halos = list(itertools.product(*trimmed_halos_per_dim))
return(blocks, haloed_blocks, trimmed_halos)